The goal of this research project is to discover the diagnostic yield and cost-effectiveness of a thorough evaluation designed to detect reversible causes of dementia in the elderly. Furthermore, the study will assess the outcome of dementia and the degree to which treatment of "reversible" dementia improved cognitive function and patient outcome. 200 patients with dementia will be systematically evaluated for reversible causes of dementia and for treatable concomitant medical illnesses. Following this diagnostic evaluation, appropriate therapy will be instituted and patients will be followed. Severity of dementia and functional impairment will be assessed initially and at intervals following the initial evaluation for a total of at least 18 months. Diagnostic yields for the diagnostic procedures will be calculated. Results of clinical presentation (history, physical examination and neuropsychiatric examinations) will be correlated with results of diagnostic evaluations and patient outcomes. Efficient and cost-effective diagnostic strategies will be developed. Profiles of patients with increased likelihood to have cognitive deficits based on treatable, reversible medical illnesses will be described.